FUELS

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Introduction

Why do we study about Fuel for IC Engine?

Because fuel properties affect the combustion process in engine

and its operation

Engines are designed to run on fuels that meet certain standards

in terms of chemical and physical properties

Quality of fuel can affect engine durability

To understand the attendant ill-effect of fuels that used for IC

engine on environment and human health

Depletion of petroleum based fuel for IC Engine from time to time

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Introduction 3

Basics of Combustion

Introduction

In order to generate Heat, Combustion of Fuel are required

Therefore the fundamental knowledge of different types of Fuelcharacteristics is essential in order to understand the combustionprocess

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Fuel+ Air Flue Gas+ HeatCombustion

Introduction

Fuel used currently for IC engines and some of its associated aftermaths: pollution, global warming and resource constraints

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Environment & Energy Restriction

Global warming problem

To minimize global warming severe reduction of CO2 emission into theatmosphere has become universal agenda

Air pollution problem

Reduction of toxic substances from vehicle has become a vital issues such as

Carbon monoxide (CO), Sulfur dioxide (SO2 ), Nitrogen dioxide (NO2 ), and

Particulate matter, PM2.5

Resource and energy problem

Transportation sector’s overdependence on petroleum must be reduced(adaptation of alternative fuels is necessary, etc.)

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Air Pollution Issue of SI engine7

The above motives can be achived through engine modification, after treatment , fuel reformation and adaptation of alternative fuel

TWC convertor8

Air Pollution Issue of CI Engine9

The above motives can be achived through engine modification,after treatment, fuel reformation and adaptation of alternativefuels

Fuels for Engines

IC Engines can be operated on different types of fuels

1. Gaseous

2. Liquid

3. Originally solid also but now very rarely used.

May be1. Naturally available or

2. Artificially derived

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Solid Fuels

Solid fuels have little practical application at the presentbecause of

Problem of handling

Disposing of the solid residue or ash

Feeding are quite cumbersome

Therefore this fuels have become unsuitable for I.C Engineapplication.

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Gaseous Fuels

Gaseous Fuels are ideal and pose very few problems inusing them in IC engine

Main gaseous fuels for engines are

Natural gas – from nature

Liquefied Petroleum Gas - from refineries

Producer gas - from coal or biomass

Biogas - from biomass

Hydrogen – from many sources

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Gaseous Fuels

Advantages of Gaseous Fuels

Mix more homogeneously with air

Eliminate starting problems

Disadvantage

Storage and handling Problem

Therefore gaseous fuels are commonly used for stationary powerplants located near the source of available of the fuel.

Some of the gaseous fuel can be liquefied under pressure forreducing the storage volume but this arrangement is veryexpensive and risky

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Natural gas14

Found compressed in porous rock and shale formations sealed in rock layer underground.

Frequently exists near or above oil deposits.

Is a mixture of hydrocarbons and non hydrocarbons in gaseousphase or in solution with crude oil.

Raw gas contains mainly methane (60-90 %) plus lesser amountsof ethane, propane, butane and pentane, negligible sulfur,nitrogen, carbon dioxide and helium are present.

Natural Gas

Natural Gas may be used as

• Liquefied Natural Gas (LNG).

• Compressed Natural Gas (CNG).

Natural Gas can be made artificially called substitute, or

synthetic or Supplemental Natural Gas (SNG).

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Natural gas

Preparation of Natural Gas

1. Separation of liquid and gas. Liquid may be a hydrocarbonpresent in the gas well along with the gas.

2. Dehydration. Water is corrosive and hydrates may form which willplug the flow. Water will also reduce the calorific value of the gas.

3. Desulfurization. Presence of hydrogensulfide is undesirable. Thegas is called sour. When the sulfur is removed the gas issweetened.

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Natural Gas

Composition

90-95% methane0-4% nitrogen,4% ethane and1-2% propane.

Advantages of Natural Gas Methane is a greenhouse gas with a global warming potential

approximately 4 times that of carbon dioxide. Its C/H ratio is lower than that of gasoline so its CO2 emissions

are 22-25% lower (54.9 compared to 71.9 g CO2/MJ fuel). Has higher calorific values

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Comparison of CNG with Gasoline

Calorific Values (Kcal/kg)

Octane Number

Auto-ignition Temp (oC)

Gasoline 10, 400 92 390

Diesel 10, 200 low 280

CNG 11, 200 130 640

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Natural Gas

If an engine is switched to CNG from gasoline, the non-methane

organic gases like CO and NOx, all reduced by 30-60%.

Toxic emissions like benzene, butadiene and aldehydes were much

less than with gasoline.

Natural gas can replace diesel fuel in heavy-duty engines with the

addition of a spark ignition system.

Engines operate at φ = 0.7 giving low in-cylinder temperatures and

hence low NOx.

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Natural Gas in Engines

Heavy-duty natural gas engines are designed to meet low emission vehicle

(LEV) emission standards without a catalytic converter and will meet ULEV

emission standards with a catalytic converter.

For heavy-duty applications, dual fuel operation is attractive, for buses,

locomotives, ships, compressors and generators. They are operated lean to

reduce NOx.

However, at light loads, the lean combustion conditions will degrade the

combustion process increasing HC and CO emissions.

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Component Percentage

Hydrogen 20

Carbon Monoxide 19.5

Carbon Dioxide 12.5

Methane 2

Nitrogen 46

Octane Number 100-105

Lower Heating Value 6.7 MJ/m3

Typical Composition of Producer gas

Energy density of stoichiometric fuel-air mixture

Producer gas: 2.5 MJ/m3

Gasoline-air: 3.5 MJ/m3

Diesel-air: 3.3 MJ/m3

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Liquid Fuels

The three commercial types of liquid fuels are

Benzol- a by product of high temperature coal carburization andconsist principally of benzene (C6H6) and toluene (C7H8)

Alcohol- used as a fuel after blending it with gasoline

Petroleum Products- the main fuels for IC engines (gasoline,

kerosene, diesel oil)

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Liquid Fuels

In most of the modern IC engines, liquid fuels are being used,

which are derivatives from liquid petroleum.

Crude petroleum consists of

A mixture of large number of hydrocarbons

Small amounts of sulphur, oxygen, nitrogen, and

Impurities such as water and sand

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Liquid hydrocarbon fuels

The basic families of liquid hydrocarbon fuels, their generalformula and their molecular structure is shown in table below

Family General Formula Molecular Arr.

Paraffin CnH2n+2 Chain

Olefin CnH2n Chain

Diolefin CnH2n-2 Chain

Naphthene CnH2n Ring

Aromatic CnH2n-4 Ring

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Paraffins (Alkanes)

Consists of a straight chain (open chain) molecular structure like methane, ethane, propane etcE.g. Butane

Suffix “ane”

The valence of each carbon atom is fully utilized in combining, by a single bond, with other carbon atoms and with hydrogen atoms.

They are termed as saturated compounds and characteristically very stable

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Branch-chain paraffin

Branch-chain paraffin has the same general chemical formula as thestraight-chain paraffin but a different molecular structure anddifferent physical characteristics and are called isomers.

E.g. Isobutane

Branch chain paraffins have good anti-knock qualities when used as SI engine fuels

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Olefins (Alkenes)

Are chain compounds similar to paraffins

Are unsaturated because they contain double bond like butene

Are not stable due to the presence of the double bond

E.g. butene

suffix “ene”

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Diolefins (Alkadiene)

Are essentially olefins with two double bonds or triple bond

Are unsaturated and rather unstable

Tend to form gum deposits during storage by reacting with oxygen

E.g. butadiene

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Napthenes or Cycloparaffins

Have the same general formula as olefins but with a ring structure

Are often formed as Cyclo-paraffins

Are saturated, and tend to be stable

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Aromatics

are ring structure compounds based on the benzene ring

While the double bonds indicate unsaturation, a peculiar nature ofthese bonds causes this family to be more stable than the otherunsaturated families

E.g. Benzene

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General Characteristics

The above families of hydrocarbons exhibit general characteristics due totheir molecular structure which are summarized below

Normal paraffins exhibit the poorest antiknock quality when used inSI engine. But the antiknock quality improves with the increasing

number of carbon atoms and

the compactness of the molecular structure.

The aromatics offer the best resistance to knocking in SI Engines.

For CI engines, the order is reversed i.e. the normal paraffins are the best fuels and

aromatics are the least desirable,

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General Characteristics

As the number of atoms in the molecular structure increases, theboiling temperature increases.

Thus fuels with fewer atoms in the molecule tend to be morevolatile.

The heating value generally increases as the proportion ofhydrogen atoms to carbon atoms in the molecule increases due tothe higher heating value of hydrogen than carbon.

Thus, paraffins have the highest heating value and the aromaticsthe least.

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Oxygenated Fuels

Alcohol There is hydroxyl radical –OH in the molecules Example: Methanol, Ethanol Ethers – ignition improvers for diesels Dimethylether (DME) – proposed as a bio diesel fuel (CH3)2O Methyl tertiary butyl ether (MTBE)

(CH3)3COCH3 – Octane improvement in gas gasoline engines

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Oxygenated Fuels

Methanol CH3OH

Ethanol C2H5OH

OHHCCOOHC

OHCOHOHCmaltoseOHCwaterstarch

onfermentati

enzyme

enzyme

5226126

61262112212

112212

22

glucose)(2

)(

+ →

→+

→+

2324 HOHCHOHCH +→+

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CRUDE OIL

Crude oil found in rock formations that were floors of oceans thousands ofthousand years ago

Organic matter trapped by rocks and subjected to high pressure andtemperatures

A mixture of water, dirt, and many different hydrocarbons of various molecularshapes and sizes

Date of first oil well drilling in USA: 1859, Titusville, PA

Most fuels are a mixture of hydrocarbons CxHy, typically 86 % C and 14% H byweight

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Composition of typical crude oil

Carbon: 80-89%

Hydrogen: 12-14%

Nitrogen: 0.3-1.0%

Sulfur: 0.3-3.0%

Oxygen: 2.0-3.0%

Plus

oxygenated compounds like phenols, fatty acids, ketones

metallic elements like vanadium and nickel.

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Typical Petroleum Refinery Products

Product Boiling Range, oCLiquefied Petroleum Gas (LPG) -40 to 0Motor Gasoline 30-200Kerosene, jet fuel 170-270Diesel Fuel 180-340Furnace Oil 180-340Lube Oils 340-540Residual Fuel 340-650Asphalt 540+Petroleum Coke Solid

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Refinery processes

1. Distillation

2. Cracking

3. Reforming

4. Polymerization

5. Alkylation

6. Isomerization

7. Hydrogenation

Raw Mat. ProductsD

istill

atio

n

Con

vers

ion

Proc

ess

Blen

ding

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Fractional Distillation

Separating using boiling point temperature.

Liquid petroleum vaporized at 6000C

The vapor admitted to fractionating tower at its bottom

The vapor is forced to pass upward along a labyrinth-like arrangement

The vapor with higher boiling point condensed out at lower levels

while those with lower boiling point moves up higher levels where they get condensed at appropriate temperature

The factional distillation can be done

Atmospheric

Vacuum

Continues (Gas separation and stabilization)

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Fractional Distillation

Fractions with low boiling

points condense at the top

Fractions with high boiling

points condense at the bottom

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Cracking Process

Braking down large and complex hydrocarbons molecules intosimpler compounds.

Thermal Cracking

Large hydrocarbon molecules at height temperature and pressureare decomposed in to smaller, lower boiling point molecules

Catalytic Cracking

Using catalysts at relatively lower pressure and temperaturethermal cracking Naphthenes are cracked to olefins and paraffins Olefins to isoparaffins needed for gasoline

Catalytic cracking gives better antiknock property for gasoline ascompared to thermal cracking

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Refinery Processes

Hydrogenation/ Hydrocracking

Cracks and adds hydrogen to molecules, producing a more saturated,

stable, gasoline fraction under high pressure and temperature.

Isomerisation Changing the relative position of the atoms within the molecule of a

hydrocarbon without changing its molecular formula.

Converting straight chain hydrocarbons into branched isomers

Example

Converting n-butane in to iso-butane for alkylation

Conversion of n-pentane and n-hexane in to isoparaffins to improve knock

rating of highly volatile gasoline

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Refinery Processes

Reforming converts saturated, low octane (low antiknock quality), hydrocarbons into

higher octane product containing about 60% aromatics.

It doesn’t increase the total gasoline volume

Alkylation Combines an olefin with an iso-paraffin to produce a branched chain iso-

paraffin in the presence of a catalyst

reacts gaseous olefin streams with iso-butane to produce liquid high octane

iso-alkanes.

Example butylene + iso butane iso-octane

alkyation

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Alternative Fuels46

The Need for Alternative Fuels

Energy Security Peak Oil- the world’s production of oil is close to its peak

Global warming concerns and the need to reduce C02 emissions which is

currently about one pound per mile for every vehicle

Air Pollution HC, CO, SO2, NOx

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Types of Alternative Fuels

1. Natural gas (Methane)

2. Methane or compressed natural gas (CNG)

3. Liquefied petroleum gas (LPG) – propane, butane & ethane

4. Alcohol

1. Methanol

2. Ethanol

5. P-series (Ethanol, Methyl-tetra-hydro-furon, (MTHF), Natural gas liquids, (pentanes, Butane)

6. Bio-diesel

7. Biogas

8. Hydrogen

9. Electricity

10. Fuel Cell

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Pros & Cons of Alt. Fuels49

Challenges of Alt. Fuels

Both economy and engineering reasons.

Cost of alternative fuel per unit of energy delivered can be greater than gasoline or diesel fuel.

The energy density of alternative fuels by volume is less than gasoline or diesel fuel.

Today the alternative fuelled engines can be modified or retrofittedengines that were originally designed for gasoline or diesel fuelling.

They are, therefore not the optimum design for the other fuels.

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LPG

Propane (C3H8) is a saturated paraffinic hydrocarbon. When blended withbutane (C4H10) or ethane (C2H6), it is designated as liquefied petroleum gas(LPG).

LPG is obtained as a by-product from: The lighter hydrocarbon fractions produced during the crude oil refining. The heavier components of wellhead natural gas.

A common LPG blend is P92, which is 92% propane and 8% butane.

Propane has an octane number of 112 (RON), so it can raise the compressionratio.

Propane requires about 5o spark advance at lower engine speeds due to itsrelative low flame speed.

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Natural Gas

Like propane, natural gas is delivered to the engine through a pressureregulator, either a mixing valve located in the intake manifold, portfuel injection at about 750 kPa, or direct injection into the cylinder.

Bi-fuel engines

Recent R&D work has included development of bi-fuel vehicles that can operated with natural gas and gasoline or natural gas and diesel.

One advantage of a bifuel operation is that the operating range of a vehicle is extended in comparison with a dedicated natural gas.

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Natural Gas

Advantage of Natural gas RON of 120, which makes it a very good SI engine fuel. One

reason for this high RON is a fast flame speed. Engines canoperate with a high compression ratio.

Low engine emissions, Less aldehydes than with methanol, andless CO2.

Fuel is fairly abundant worldwide. It can be made from coalbut this is more costly.

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Natural Gas

Disadvantage of Natural gas Low energy density resulting in low engine performance.

Low engine volumetric efficiency because it is a gaseous fuel same reason asLPG.

Need for large pressurized fuel storage tank. Most test vehicles have a rangeof only 200 km. There is some safety concern with a pressurized fuel tank.

Inconsistent fuel properties

Refueling is slow process.

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Alcohol

Alcohols are an attractive alternative fuel because they can beobtained from a number of sources, both natural andmanufactured.

The two kinds of alcohol that seems most promising and havehad the most development as engine fuel.

Methanol (Methy Alcohol) and

Ethanol (Ethyl Alcohol)

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Methanol

Pure methanol is labelled M100, and a mix of 85% methanol and15% gasoline is labeled M85.

M85 has an octane rating of 102.

The cetane number of methanol is low at about 5, but it can be used incompression ignition engines with diesel fuel pilot ignition.

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Ethanol

Ethanol (C2H5OH) is an alcohol fuel formed from thefermentation of sugar and grain stocks, primarily sugar caneand corn, which are renewable energy source

Ethanol is a liquid at ambient conditions, and non-toxic at low concentration.

Gasohol (E10) is a gasoline-ethanol blend with about 10%ethanol by volume.

E85 is a blend of 85% ethanol and 15% gasoline.

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Advantage of Alcohol

It can be obtained from a number of sources, both naturaland manufactured.

It is a high octane fuel with anti-knock index number of over100.

Engine using high-octane fuel can run more efficiently byusing higher compression ratio.

Generally lower overall emissions

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Advantage of Alcohol

When burned, it forms more moles of combustion, whichgives higher pressure and more power in the expansionstroke.

It has high evaporative cooling which result in a coolerintake process and compression stroke, Raised volumetricefficiency and reduced required work input.

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Disadvantage of Alcohol

Low energy content of the fuel. This mean that almost twice asmuch alcohol as gasoline must be burned to give the same energyinput to the engine.

But the power would be the same, as the lower air-fuel rationeeded by alcohol.

More aldehydes in the exhaust. If as much alcohol fuel wasconsumed as gasoline, aldehyde emissions is a serious problem.

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Disadvantage of Alcohol

Much more corrosive than gasoline on copper, brass,aluminum, rubber, and many plastics.

In this context, it puts some restrictions on the design andmanufacturing of engines to be used with this fuel.

Poor cold weather staring characteristics due to low vaporpressure and evaporation.

Poor ignition characteristics in general.

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